1. Field of the Invention
The lens described in this disclosure relates to ophthalmoscopic lenses for use with the slit lamp or other biomicroscope. More particularly the invention relates to diagnostic and therapeutic gonioscopic and indirect ophthalmoscopic contact lenses that incorporate two reflecting surfaces which combine to provide positive power contributing to the formation of a real image of the examined structures of the eye anterior of the lens or within the lens or element of the lens while optimally directing the light rays to the objective lens of the slit lamp biomicroscope for stereoscopic viewing and image scanning.
2. Description of Prior Art
Eye examination lenses including indirect and direct ophthalmoscopy and gonioscopy lenses are used by ophthalmologists and optometrists for the diagnosis and treatment of the internal structures of the eye in conjunction with a slit lamp or other biomicroscope. Indirect ophthalmoscopy lenses, such as the Volk 90D lens, generally comprise a single lens with two refracting surfaces which combine to provide positive power contributing to the formation of a real image of the patient's eye fundus anterior of the examined eye. Direct ophthalmoscopy lenses, such as the Hruby lens, use minus power to produce a virtual image of the patient's eye fundus generally posterior of the examination lens. Some indirect and direct ophthalmoscopic lenses are pre-set or hand held in front of the patient's eye while others incorporate a contacting means and interface with the cornea and tear layer of the eye. An example of a contact indirect ophthalmoscopy lens would be the Volk QuadrAspheric lens and an example of a contact direct ophthalmoscopy lens would be the Volk Centralis Direct lens. Indirect ophthalmoscopy lenses provide a wide field inverted view while direct ophthalmoscopy lenses provide a small field with high magnification and high resolution in correct orientation.
Diagnostic lenses such as the Goldmann lens, Zeiss four mirror gonioscopy lens and Keoppe lens contact the eye and are used to examine and treat structures of the anterior chamber of the eye, specifically in the area of the anterior chamber angle, or iridocorneal angle. The four mirror lens incorporates angulated mirrors and like the other gonioscopy lenses operates to eliminate the power of the cornea to avoid total internal reflection of the light rays at the cornea-air interface. Light rays from the anterior chamber angle enter the lens and are reflected by mirrors along the line of vision of the viewer, one for each quadrant of the examined eye. In that a single mirror is used for each of the four sectional views, each image is reverted and discontinuous from the other sectional views. Furthermore the field of view obtainable through each mirror is very small. The Goldmann lens performs in an identical manner to the Zeiss four mirror lens except that it has only a single mirror used for gonioscopy. The Keoppe lens employs a contact lens having a rather highly curved convex anterior surface and a thickness sufficient to prevent total internal reflection of incident light rays from the anterior chamber angle from its convex surface, thereby allowing light rays to pass through for examination purposes. There is no real conjugate pupil formed by the Keoppe lens and the physician may only obtain a small field of view at an extremely angled inclination relative to the eye axis through a stereoscopic viewer.
Real image forming ‘indirect ophthalmoscopic’ viewing systems have also been suggested for viewing structures of the anterior chamber. An advantage of such a system lies in the continuous and uninterrupted field of view that may be provided in the form of an annular section corresponding to the structures of the anterior chamber angle, viewed with the slit lamp biomicroscope in its normal orientation. Such a system is described in U.S. Pat. No. 6,164,779 to Volk. This patent sets forth a series of lenses comprising a first corneal contacting lens system receiving light rays originating at the anterior chamber angle and a second imaging forming system receiving light rays from the first lens system producing a real image of the anterior chamber angle outside of the patient's eye. Various embodiments include refracting as well as reflecting surfaces providing positive power for focusing light rays. Although the U.S. Pat. No. 6,164,779 patent presents the first real image forming gonioscopy lens system of its day, the complexity of a number of embodiments as well as an insufficiency of others to provide correction of chromatic and other aberrations prevented commercialization of this invention. U.S. Pat. No. 7,144,111 to Ross, III, et al., represents an attempt to provide an improved real image forming gonioscopy lens. Although achromatized and corrected for other aberrations, the lenses depicted in the embodiments of the 111 patent exhibit numerous disadvantages that preclude its successful application, including excessive weight, an excessive lens length of over 35 mm, an excessive distance from the examined eye to the image plane of over 51 mm, which is beyond the positioning range of the slit lamp biomicroscope, and poor stereoscopic visualization and image scanning capability resulting from the small light ray footprint at the biomicroscope objective lens aperture.